Enhanced visible-light photocatalytic bacterial inhibition using recyclable magnetic heterogeneous nanocomposites (Fe3O4@SiO2@Ag2WO4@Ag2S) in core/shell structure

Abstract

In this work, a novel core/shell heterogeneous nanocomposite photocatalyst (Fe3O4@SiO2@ Ag2WO4@Ag2S) was prepared using multistep methods. Several characterization techniques were conducted to analyze the synthesized core/shell magnetic nanocomposites, such as XRD, FE-SEM, TEM, UV-DRS, and VSM. The photocatalytic bacterial inactivation activity of synthesized photocatalysts (Fe3O4@SiO2@Ag2WO4, Fe3O4@SiO2@Ag2S, Fe3O4@SiO2@Ag2WO4@Ag2S, Ag2WO4, Ag2S) was investigated against Escherichia coli (E. coli) bacterium under a visible light source. The synthesized Fe3O4@SiO2@Ag2WO4@Ag2S showed enhanced photocatalytic inactivation activity (approximately 9.5-log reduction) after 105 min of irradiation time. This result is attributed to increasing the photo-generated electron-hole separation by forming a heterojunction between the two photoactive semiconductors (Ag2WO4 and Ag2S) in one system. The kinetic studies revealed that the Fe3O4@SiO2@Ag2WO4@Ag2S exhibited the best E. coli inactivation activity with a constant rate value (kapp/min−1) of 0.07393 min−1, which is 1.4 and 1.7 times greater than that of pure Ag2S and Ag2WO4, respectively. The effects of different parameters on the photocatalytic microbial inactivation were examined, such as initial microbial concentration, catalyst dose, and pH of the solution. The scavenger studies confirmed the important roles of reactive species (H2O2, •O2–, h+) in the photocatalytic reaction. The photocatalytic mechanism of Fe3O4@SiO2@Ag2WO4@Ag2S was well explained by p-n heterojunction based on DRS analysis and scavenger experiments of reactive species. The stability and recyclability studies proved that the Fe3O4@SiO2@Ag2WO4@Ag2S sample is highly stable and easy to separate by the external magnet, which can be used many times as antibacterial agents without significant losses in their photocatalytic activity.